The present invention relates to respiratory care devices, and specifically to a heater for use with respiratory nebulizers which produce an aerosol to be delivered to the patient.
In conventional respiratory care systems including nebulizers, oxygen is mixed with a liquid, usually sterile water, saline solution or other respiratory solution to form an aerosol which is passed through a flexible feed tube and ultimately delivered to the patient through a face mask. A recent trend in respiratory therapy is to provide a heated aerosol to the patient to minimize stress on the patient's respiratory system.
Conventional nebulizer heaters have concentrated on heating the supply of sterilized water prior to the nebulization process. However, a significant drawback to this approach is that the water loses heat in the nebulization process. In addition, the tube through which the aerosol passes to reach the patient is usually cooler than the temperature of the heated water. Consequently, as the heated aerosol progresses through the tube, condensation appears on the inside of the tube. As the treatment continues, the tube eventually fills with condensate water, prematurely cooling the aerosol and wasting heat. Attempts to heat the tube instead of the water have been abandoned as being ineffective or impractical.
Another unsolved design parameter of nebulizer heaters is that when heat is cyclically applied to the aerosol, a so-called "spike effect" results, in which excessive heat is applied to achieve a target temperature, but instead exceeds the target due to the cumulative effect of the applied heat. The control circuitry then responds by reading the higher temperature and shutting off the heat, thus causing the temperature of the aerosol to prematurely plummet.
In addressing the above-identified drawbacks of conventional nebulizer heater systems, an important design parameter to be considered is that if too much heat is applied to an aerosol, the moisture content will decrease to the point that the aerosol's therapeutic benefits are neutralized. Accordingly, enough heat must be applied to prevent condensation and to provide the patient with an adequately heated aerosol, while avoiding overheating the aerosol to the point of desiccating it.
Another important design factor is that any heat applied must be accurately monitored to maintain a constant temperature of the aerosol reaching the patient, and to avoid spiking.
Thus, there is a need for a nebulizer heater which delivers heated aerosol to the patient within a specified temperature range to provide the therapeutic benefits of heated aerosols. There is a further need for a nebulizer heater which accurately monitors the aerosol temperature at the point the patient receives the aerosol, and which adjusts the aerosol temperature in a manner which avoids spiking. There is also a need for such a nebulizer heater which can be readily adapted to existing nebulizer systems for accurate, safe and energy efficient operation.